The present invention relates to tiltmeters, and has particular relation to tiltmeters which are self-errecting.
A tiltmeter is a high technology version of a carpenter's level. Like a carpenter's level, it measures how far the meter has tilted by the position of a bubble in a fluid against a curved upper surface. Unlike a carpenter's level, it measures it by comparing the conductance of the fluid (which is very sensitive to the position of the bubble) between a centrally located anode on the bottom of the meter and two cathodes on opposite sides of the top of the meter. Since the relative conductances can be measured with great accuracy, the amount of tilt can be measured with corresponding accuracy.
In some applications, it is important to know how far from vertical the apparatus to which the tiltmeter is attached has leaned. In this case, the meter must be precisely aligned with the appropriate axis of the apparatus, and the apparatus must, in turn, be precisely aligned in a vertical direction. In other situations, to which the present invention is directed, it is not necessary for the tiltmeter to measure the absolute angle made between the apparatus and the vertical. In these situations, the tiltmeter need only measure changes in the angle, having a certain minimum angular velocity. For example, when measuring the strength of an earthquake, it is important to know not only how far the earth slipped, but also how much it tilted and how quickly it returned to normal as the shock wave passed through it. This may be a much more important factor to consider, when designing a road or parking lot, than how much the road or parking lot moved as a unit. At the same time, it is not important that the road or parking lot be absolutely level to within a few seconds of arc. It is important to know only how much it was twisted during the earthquake. In such cases, it is an advantage for the tiltmeter to be able to be set onto, or built into, the road in an only roughly vertical orientation, and, in a reasonable time, get quite close to true vertical.